1. Field of the Invention
The present invention relates to a semiconductor device and an active matrix substrate which is improved in the electrode or wiring thereof. The present invention also relates to a process for producing the semiconductor device or the active matrix substrate.
2. Related Background Art
Semiconductor devices usually have wiring for connecting the semiconductor substrate or the semiconductor layer with an external circuit. The wiring is generally made by Al (aluminum). An example of the process for Al wiring or Al electrode formation is Damascene Process employing CMP (chemical mechanical polishing) reported in '94 VLSI Symp. This process is explained below by reference to FIGS. 14A to 14D. In FIGS. 14A to 14D, a thermal oxidation film 61, and an insulating interlayer film 62 are formed on a silicon substrate 60 (FIG. 14A). The insulating interlayer film 62 is patterned to form an Al-embedding pattern 63 (FIG. 14B). Thereon, an Al film 64 is formed by sputtering (FIG. 14C) in a thickness larger than the height of the Al-embedding pattern. Then the Al film 64 is polished by a CMP method to form an Al electrode 65 (FIG. 14D).
In the wiring or electrode formation by the Damascene process described above, the Al electrode 65 is concaved and becomes thinner in the middle portion of disadvantageously as shown in FIG. 15E. This thinning is called dishing. This dishing is caused by non-uniform polishing owing to difference of CMP polishing rates between the material of the metal layer such as Al and the material of the insulating layer such as p-SiO coexisting in one and the same polishing plane, and deformability of the polishing cloth. The material of a higher polishing rate is polished more. The polishing rate of Al is four or five times as high as that of p-SiO, resulting in dishing of the Al electrode 65. The degree of dishing increases with increase of the size of the Al electrode as shown in FIG. 16, and at the size of 300 .mu.m of the Al electrode the dishing can reach about 3000 .ANG.. When the Al electrode is in a size of several hundred .mu.m like the portion of a wire bonding pad, the Al electrode 65 can be partly removed by excessive dishing to render the wire bonding impracticable and to lower productivity of elements. Further, in Al wiring, the dishing increases the resistance of the wiring to deteriorate the properties of the devices.